Alkali-free sealing glasses for molybdenum

ABSTRACT

SiO 2  -Al 2  O 3  -alkaline earth oxides glass compositions suitable for glass/molybdenum sealings with high thermal load capability, having coefficients of thermal expansion in the temperature range of 20°-300° C. of 4.6-5.1×10 -6  /° C., glass transformation temperatures (Tg) of 775°-810° C., softening temperatures (Ew) greater than 930° C., processing temperatures (V A ) of 1232°-1273° C. and at length of V A  -Ew greater than 300° C. as regards processing technology of these glasses in the mixture, which consist essentially of the following components, computed as percent by oxide weight: 
     
         ______________________________________                                    
 
    
     SiO 2           57.00-64.00                                            
                             wt %                                         
Al 2  O 3    12.50-16.50                                            
                             wt %                                         
ZrO 2           1.00-5.50 wt %                                         
Al 2  O 3  + ZrO 2                                               
                   15.00-19.00                                            
                             wt %                                         
CaO                11.50-19.20                                            
                             wt %                                         
BaO                0-6.50    wt %                                         
CeO 2           0-8.00    wt %                                         
TiO 2           0-4.50    wt %                                         
CaO + BaO + CeO 2  + TiO 2                                          
                   18.60-25.70                                            
                             wt % and                                     
As 2  O 3    0-0.30    wt %                                         
______________________________________

DESCRIPTION OF THE INVENTION

1. Technical Field of the Invention

This invention relates to alkali-free, silicate sealing glasses having thermal expansion coefficients # of 4.6-5.1×10⁻⁶ /°C. and transformation temperatures (Tg) of 775°-810° C., which are accordingly suitable for sealing with molybdenum and therefore useful, e.g., for the manufacture of so-called halide lamps and/or halide-containing filament lamps with regenerating cycles which have a high thermal load capability.

2. Background Art

SiO₂ -Al₂ O₃ -alkaline earth oxide glass compositions have been described in DOS No. 27 33 169 for seals with molybdenum; these familiar glasses are, however, poorly suited for machine tube or pipe manufacturing.

DISCLOSURE OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a glass composition useful for machine tube manufacturing.

Another object of the present invention is to provide glass compositions having a low devitrification tendency.

A further object of the present invention is to provide glass compositions suitable for sealing with molybdenum to form a seal having excellent mechanical strength during continuous or successive use.

An additional object of the present invention is to provide glass compositions which are colorless or yellow and useful in halide or halide-containing filament lamps.

A more particular object of the present invention is to provide yellow halide lamps which do not require the use of any additional filter glasses.

Upon study of the specification and appended claims, further objects, features and advantages of the present invention will become more fully apparent to those skilled in the art to which this invention pertains.

Best Mode for Carrying Out the Invention

Briefly, the above and other objects, features and advantages of the present invention are attained in one aspect thereof by providing SiO₂ -Al₂ O₃ -alkaline earth oxides glass compositions suitable for glass/molybdenum sealings with high thermal load capability, having coefficients of thermal expansion in the temperature range of 20°-300° C. of 4.6-5.1×10⁻⁶ /°C., glass transformation temperatures (Tg) of 775°-810° C., softening temperatures (Ew) greater than 930° C., processing temperatures (V_(A)) of 1232°-1273° C. and a length of V_(A) -Ew greater than 300° C. as regards processing technology of these glasses, which consist essentially of the following components, computed as percent by weight oxide:

    ______________________________________                                         SiO.sub.2          57.00-64.00                                                                              wt %                                              Al.sub.2 O.sub.3   12.50-16.50                                                                              wt %                                              ZrO.sub.2          1.00- 5.50                                                                               wt %                                              Al.sub.2 O.sub.3 + ZrO.sub.2                                                                      15.00-19.00                                                                              wt %                                              CaO                11.50-19.20                                                                              wt %                                              BaO                0- 6.50   wt %                                              CeO.sub.2          0- 8.00   wt %                                              TiO.sub.2          0- 4.50   wt %                                              CaO + BaO + CeO.sub.2 + TiO.sub.2                                                                 18.60-25.70                                                                              wt % and                                          As.sub.2 O.sub.3   0- 0.30   wt %                                              ______________________________________                                    

As additional characteristic features, these glasses have softening temperatures (Ew) of 936°-969° C., processing temperatures (V_(A)) of 1232°-1273° C., densities of 2.638-2.767 g/cc, and T_(K) 100-values of about 600° C. From this difference of V_(A) -Ew results a processing technology length of greater than 300° C. for the glasses. This causes them to be better suited for machine tube manufacturing (e.g. Danner-traction) than similar familiar but usually shorter glasses for which V_(A) -Ew is less than 300° C.

Finally, it is advantageous for manufacturing that the glasses of the present invention have a lower devitrification tendency. The glasses of this invention exhibit only a weak surface devitrification in the temperature range of 1020°-1300° C. with the maximum between 1150°-1250° C. and crystalline growth speeds of 0.05-0.40 mm/min. determined in accordance with the gradient method with a temper period of 60 minutes described in Glastechn. Ber. 41(4): 138-145 (1968).

The range of compositions of the present invention permits the manufacture both of clear (i.e., colorless in a technical sense) glasses as well as glasses with a yellow coloring or tinting. These yellow glasses therefore permit the direct manufacture of yellow light halide lamps in an advantageous manner without the use of any additional filter glasses. Yellow tinting of the glasses of the invention is achieved by the simultaneous introduction CeO₂ in the form of the hydrate and of TiO₂, with the sum of CeO₂ +TiO₂ of 7.67-12.26 percent by weight and a ratio of CeO₂ :TiO₂ of 1.56-2.29. The transmission values of these glasses in the visible range for a layer thickness of 0.5 mm lie between 60 and 85%. Yellow glasses of this type have not been known in the prior art.

The fusion stresses of glasses according to the invention towards molybdenum (strain double refraction, represented as optical path difference in nm/cm), range from weak tensile stresses (negative signs) to the range of compressive stress (positive sign), i.e. from -12 nm/cm to +300 mn/cm. These values assure a perfect mechanical strength of such a molybdenum glass compound during continuous or sustained use.

It is generally desirable to utilize the familiar effect of ZrO₂ which increases viscosity; however, ZrO₂ at the same time has been known for its extremely poor solubility. Surprisingly, it has been found that, by simultaneously introducing considerable quantities of CaO, the solubility of ZrO₂ is strongly improved in glasses of the system. The solubility promoting effect of CaO on ZrO₂ is therefore an essential feature of the glasses of the invention, which avoids the normally poor solubility of ZrO₂ while simultaneously using the strong viscosity promoting effect of ZrO₂ for increasing the Tg.

The glasses in accordance with this invention are characterized by the following ranges of composition, expressed in percent by weight:

    ______________________________________                                         Range for Clear (Colorless) and Yellow Glasses:                                ______________________________________                                         SiO.sub.2        57.00-64.00                                                                              wt. %                                               Al.sub.2 O.sub.3 12.50-16.50                                                                              wt. %                                               ZrO.sub.2        1.00- 5.50                                                                               wt. %                                               Al.sub.2 O.sub.3 + ZrO.sub.2                                                                    15.00-19.00                                                                              wt. %                                               CaO              11.50-19.20                                                                              wt. %                                               BaO              0- 6.50   wt. %                                               CeO.sub.2        0- 8.00   wt. %                                               TiO.sub.2        0- 4.50   wt. %                                               CaO + BaO + CeO.sub.2 + TiO.sub.2                                                               18.60-25.70                                                                              wt. % and                                           As.sub.2 O.sub.3 0- 0.30   wt. % (introduced                                                              as purifying/                                                                  refining agent).                                    ______________________________________                                    

    ______________________________________                                         Range for                                                                      Clear Glasses:                                                                 SiO.sub.2    59.00-64.00                                                                              wt. %                                                   Al.sub.2 O.sub.3                                                                            12.50-16.50                                                                              wt. %                                                   ZrO.sub.2    1.00- 5.50                                                                               wt. %                                                   Al.sub.2 O.sub.3 + ZrO.sub.2                                                                15.00-19.00                                                                              wt. %                                                   CaO          15.50-19.20                                                                              wt. %                                                   BaO          1.00- 6.50                                                                               wt. %                                                   CaO + BaO    18.60-22.70                                                                              wt. %       and                                         As.sub.2 O.sub.3                                                                            0- 0.30   wt. %       as above                                    CeO.sub.2    0- 0.20   wt. %       introduced as                                                                  purifying/                                                                     refining                                                                       agents.                                     ______________________________________                                         Yellow Glasses:                                                                SiO.sub.2    57.00-60.00                                                                              wt. %                                                   Al.sub.2 O.sub.3                                                                            14.50-15.00                                                                              wt. %                                                   ZrO.sub.2    2.00- 2.80                                                                               wt. %                                                   Al.sub.2 O.sub.3 + ZrO.sub.2                                                                16.50-17.80                                                                              wt. %                                                   CaO          11.50-15.30                                                                              wt. %                                                   CeO.sub.2    5.00- 8.00                                                        TiO.sub.2    2.70- 4.50                                                                               wt. %                                                   CaO + CeO.sub.2 + TiO.sub.2                                                                 23.00-25.70                                                                              wt. %                                                   CeO.sub.2 + TiO.sub.2                                                                       7.70-12.30                                                                               wt. %       and                                         CeO.sub.2 :TiO.sub. 2                                                                       1.56- 2.29.                                                       ______________________________________                                    

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever. In the following Examples, the temperatures are set forth uncorrected in degrees Celsius; unless otherwise indicated, all parts and percentages are by weight.

EXAMPLES 1-15

Tables 1 and 2 contain 15 examples of compositions in the range of compositions of the present invention, expressed in percent by weight, and the characteristic features of these glasses, which are prepared according to conventional techniques known for the preparation of SiO₂ -Al₂ O₃ -alkaline earth oxide glass compositions. Chromaticity diagram information is shown for Examples 11-15 from which the value for z can be calculated (since x+y+z=1); other values can similarly be readily ascertained.

                  TABLE 1                                                          ______________________________________                                         Examples of Composition in Percent by Weight                                   ______________________________________                                         Components   1       2       3     4     5                                     ______________________________________                                         SiO.sub.2    61.00   59.00   61.00 62.50 62.00                                 Al.sub.2 O.sub.3                                                                            12.50   14.50   15.00 15.00 15.00                                 ZrO.sub.2    5.50    5.00    4.00  4.00  3.50                                  CaO          17.50   15.50   16.50 17.50 18.50                                 BaO          3.50    6.00    3.50  1.00  1.00                                  CeO.sub.2    0.15            0.10  0.10  0.15                                  TiO.sub.2                                                                      As.sub.2 O.sub.3     0.30                                                      Sum of Percent                                                                              100.15  100.30  100.10                                                                               100.10                                                                               100.10                                ______________________________________                                         Appearance   Clear   Clear   Clear Clear Clear                                 ______________________________________                                         Components   6       7       8     9     10                                    ______________________________________                                         SiO.sub.2    62.30   64.00   60.00 62.00 61.50                                 Al.sub.2 O.sub.3                                                                            14.50   12.50   16.50 15.00 15.00                                 ZrO.sub.2    3.00    2.50    2.50  2.50  1.00                                  CaO          19.20   18.50   18.50 16.50 16.00                                 BaO          1.00    2.50    2.50  4.00  6.50                                  CeO.sub.2    0.15    0.20    0.20  0.20  0.20                                  TiO.sub.2                                                                      As.sub.2 O.sub.3                                                               Sum of Percent                                                                              100.10  100.20  100.20                                                                               100.20                                                                               100.20                                ______________________________________                                         Appearance   Clear   Clear   Clear Clear Clear                                 ______________________________________                                         Components   11      12      13    14    15                                    ______________________________________                                         SiO.sub.2    60.00   58.00   58.00 60.00 57.00                                 Al.sub.2 O.sub.3                                                                            15.00   15.00   15.00 15.00 14.50                                 ZrO.sub.2    2.00    2.00    2.00  2.00  2.80                                  CaO          15.30   13.50   12.70 11.50 14.20                                 BaO                                                                            CeO.sub.2    5.00    8.00    8.00  7.00  7.30                                  TiO.sub.2    2.70    3.50    4.30  4.50  4.20                                  As.sub.2 O.sub.3                                                               Sum of Percent                                                                              100.00  100.00  100.00                                                                               100.00                                                                               100.00                                ______________________________________                                                      P.              D.    D.    D.                                    Appearance   Yellow  Yellow  Yellow                                                                               Yellow                                                                               Yellow                                ______________________________________                                          P. Yellow = Pale Yellow                                                        D. Yellow = Dark Yellow                                                  

                  TABLE 2                                                          ______________________________________                                         Characteristics Values of Glasses 1- 15 of Table 1                             ______________________________________                                         Characteristics                                                                             1       2       3     4     5                                     ______________________________________                                         α×10.sup.6 (20-300° C.)/°C.                                       5.05    4.99    4.84  4.73  4.96                                  Tg(°C.,;ηca.10.sup.13.5 P                                                        797     800     800   800   800                                   Ew(°C.);η=10.sup.7.6 P                                                           940             958         969                                   V.sub.A (°C.);η=10.sup.4 Poise                                                   1255    1273    1262  1271  1270                                  V.sub.A -Ew(°C.)                                                                     315             304         301                                   Density (g/cc)                                                                              2.709           2.679 2.638 2.65                                  T.sub.K100 (°C.);ξ=10.sup.8 Ω.cm                                            609             599                                               Fusion stress towards                                                          Molybdenum (nm/cm)                                                                          +92     -12     +52   +170  +110                                  Color coordinates                                                              x, y and τ.sub.ges (%) x                                                   in accordance with y                                                           DIN 5033 for standard                                                          light C and 0.5 mm.τ.sub.ges                                               Thickness                                                                      ______________________________________                                         Characteristics                                                                             6       7       8     9     10                                    ______________________________________                                         α×10.sup.6 (20-300° C.)/°C.                                       5.10    5.03    5.03  4.92  5.05                                  Tg(°C.;ηca.10.sup.13.5 P                                                         795     783     794   810   788                                   Ew(°C.);η=10.sup.7.6 P                                                           942     950     951         966                                   V.sub.A (°C.);η=10.sup.4 Poise                                                   1242    1251    1255  1269  1268                                  V.sub.A -Ew(°C.)                                                                     300     301     304         302                                   Density (g/cc)                                                                              2.652   2.638   2.665 2.661 2.67                                  T.sub.k100 (°C.);ξ=10.sup.8 Ω.cm                               Fusion stress towards                                                          Molybdenum (nm/cm)                                                                          +11     +90     +59   +25   +162                                  Color coordinates                                                              x, y and τ.sub.ges (%) x                                                   in accordance with y                                                           DIN 5033 for standard                                                          light C and 0.5 mm.τ.sub.ges                                               Thickness                                                                      ______________________________________                                         Characteristics                                                                             11      12      13    14    15                                    ______________________________________                                         α×10.sup.6 (20-300° C.)/°C.                                       4.90    4.78    4.67  4.60  4.85                                  Tg(°C.)ηca.10.sup.13.5 P                                                         782     775     775   775   777                                   Ew(°C.);η=10.sup.7.6 P  936                                         V.sub.A (°C.);η=10.sup.4 Poise                                                           1233    1232  1236  1232                                  V.sub.A -Ew(°C.)            300                                         Density (g/cc)                                                                              2.712   2.758   2.756 2.731 2.767                                 T.sub.K100 (°C.);ε=10.sup.8 Ω.cm                          Fusion stress towards                                                          Molybdenum (nm/cm)                                                                          +92     +225    +300  +260  +215                                  Color coordinates                                                              x, y and τ.sub.ges (%) x                                                                0.3277  0.3581  0.3991                                                                               0.4165                                      in accordance with y                                                                        0.3426  0.3797  0.4198                                                                               0.4343                                      DIN 5033 for standard                                                          light C and 0.5 mm.τ.sub.ges                                                            85      74      62    60                                          Thickness                                                                      ______________________________________                                    

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those specifically used in the examples. From the foregoing description, one skilled in the art to which this invention pertains can easily ascertain the essential characteristics thereof and, without departing from the spirit and scope of the present invention, can make various changes and modifications to adapt it to various usages and conditions.

Industrial Applicability

As can be seen from the present specification and examples, the present invention is industrially useful in the manufacture of so-called halide lamps and/or halide-containing filament lamps with regenerating cycles which have a high thermal load capability. 

What is claimed is:
 1. SiO₂ -Al₂ O₃ -alkaline earth oxide glass compositions suitable for glass/molybdenum sealings with high thermal load capability, having coefficients of thermal expansion in the temperature range of 20° to 300° C. of 4.6-5.1×10⁻⁶ /°C., glass transformation temperatures (Tg) of 775°-810° C., softening temperatures (Ew) greater than 930° C., processing temperatures (V_(A)) of 1232°-1273° C. and a length of V_(A) -Ew greater than 300° C. as regards processing technology of these glasses in the mixture, which consist essentially of the following components, computed as percent by weight oxides:

    ______________________________________                                         SiO.sub.2          57.00-64.00                                                                              wt %                                              Al.sub.2 O.sub.3   12.50-16.50                                                                              wt %                                              ZrO.sub.2          1.00-5.50 wt %                                              Al.sub.2 O.sub.3 + ZrO.sub.2                                                                      15.00-19.00                                                                              wt %                                              CaO                11.50-19.20                                                                              wt %                                              BaO                0-6.50    wt %                                              CeO.sub.2          0-8.00    wt %                                              TiO.sub.2          0-4.50    wt %                                              CaO + BaO + CeO.sub.2 + TiO.sub.2                                                                 18.60-25.70                                                                              wt % and                                          As.sub.2 O.sub.3   0-0.30    wt %                                              ______________________________________                                    


2. Colorless molybdenum sealing glasses according to claim 1 which contain:

    ______________________________________                                         SiO.sub.2        59.00-64.00                                                                              wt. %                                               Al.sub.2 O.sub.3 12.50-16.50                                                                              wt. %                                               ZrO.sub.2        1.00-5.50 wt. %                                               Al.sub.2 O.sub.3 + ZrO.sub.2                                                                    15.00-19.00                                                                              wt. %                                               CaO              15.50-19.20                                                                              wt. %                                               BaO              1.00-6.50 wt. %                                               CaO + BaO        18.60-22.70                                                                              wt. %                                               As.sub.2 O.sub.3 0-0.30    wt. % and                                           CeO.sub.2        0-0.20    wt. %                                               ______________________________________                                    


3. Yellow molybdenum sealing glasses according to claim 1 which contain:

    ______________________________________                                         SiO.sub.2         57.00-60.00                                                                              wt. %                                              Al.sub.2 O.sub.3  14.50-15.00                                                                              wt. %                                              ZrO.sub.3         2.00- 2.80                                                                               wt. %                                              Al.sub.2 O.sub.3 + ZrO.sub.2                                                                     16.50-17.00                                                                              wt. %                                              CaO               11.50-15.30                                                                              wt. %                                              CeO.sub.2         5.00- 8.00                                                                               wt. %                                              TiO.sub.2         2.70- 4.50                                                                               wt. %                                              CaO + CeO.sub.2 + TiO.sub.2                                                                      23.00-25.70                                                                              wt. %                                              CeO.sub.2 + TiO.sub.2                                                                            7.70-12.30                                                                               wt. % and                                          CeO.sub.2 :TiO.sub.2                                                                             1.56- 2.29                                                                               wt. %.                                             ______________________________________                                     